Modern aircraft engines have become increasingly more efficient. Higher engine efficiencies have given rise to a need for increased heat exchanger sizes in air-to-air anti-icing systems traditionally employed on conventional jet aircraft. The larger heat exchangers have become necessary to provide enough engine core bleed air for sufficient anti-icing capability. However, continued increases of heat exchanger size can impact engine performance and engine nacelle integration.
Although liquid heat transfer mechanisms have long been recognized as more efficient than air-to-air heat transfer mechanisms, liquid systems have in the past been considered too heavy for use in aircraft, which are typically limited by operational weight constraints. However, engine energy extraction issues may require liquid systems to harvest waste heat energy from the engine. As such, the use of liquid heat exchanger anti-icing systems may now be viable for increased efficiency in commercial aircraft.
During flight, traditional air-to-air systems have required movements of large volumes of airflow through typical wing D-ducts, situated immediately behind wing leading edges, to assure up to 450 degree Fahrenheit heated air temperatures required to assure requisite BTU per hour per linear foot heat transfer for satisfactory anti-icing of wing leading edges, in accordance with icing conditions described in Appendix C of the Federal Aviation Regulations. Use of liquid heat exchangers directed to optimizing anti-icing heat transfer efficiencies should allow for use of physically smaller heat exchangers, in part compensating for any additional weight burden of liquids used. As such, liquid heat exchanger systems may potentially become more common in future large commercial aircraft.